Solid state imagers, including charge coupled devices (CCD) and CMOS imagers, are used in photo imaging applications. A solid state imager includes a focal plane array of pixels, typically arranged in rows and columns, each one of the pixels including a photosensor for accumulating photo-generated charge. A microlens is placed over a respective imager pixel and is used to focus light onto the respective photosensor. The use of microlenses significantly improves the photosensitivity of the imager by collecting light from a large light collecting area and focusing it on a small photosensitive area of the pixels. The ratio of the overall light collecting area of the photosensitive area to the overall area of the pixel is known as the “fill factor” of the pixel.
Optimally, all of the light from a pixel's overall light collecting area, including an associated microlens, will be directed to the pixel's photosensitive area. However, in practice, a phenomenon known as optical crosstalk can result when off-axis light strikes a microlens at an obtuse angle and strikes the photosensitive region of an adjacent pixel. Optical crosstalk can degrade the quality of a captured image by causing a light reading that is too low in some pixels and too high in others, and can alter color balance of an image, as light intended for one color pixel strikes the photosensitive area of a different color pixel.
Accordingly, it is desirable to have a microlens that could reduce optical crosstalk.